1. Field of the Invention:
The present invention relates to a two piece type solid golf ball formed by covering a solid core with a thermoplastic resin cover. More particularly, it relates to a solid golf ball which provides a long overall distance, improved controlability, extended durability, and good shot feeling.
2. Description of the Prior Art
There has been known a two-piece type solid golf ball formed by covering a solid core with a thermoplastic resin cover, said solid core being produced by mixing polybutadiene rubber, unsaturated carboxylic acid (such as methacrylic acid), zinc oxide and peroxide, and molding the mixture with heating. As the cover material, a hard ionomer resin is usually used because of its superiority in cut resistance. The solid golf ball having a cover of ionomer resin has superior durability and good flight performance. Moreover, in order to improve the coefficient of restitution (initial velocity at impact) of a solid golf ball, there has been proposed an idea of increasing the thickness of the ionomer resin cover to about 2.1 to 2.5 mm (Japanese Patent Laid-open Nos. 37961/1984 and 49780/1984).
However, as compared with a thread-wound golf ball, a solid ball is by far inferior in controlability required when the shot is made by a middle iron or short iron. In addition, a solid golf ball provides a poor shot feeling. For this reason, most professional golfers do not use solid golf balls in a tournament.
Proposals put forward for improving the shot feeling of conventional solid golf balls include lowering the hardness of the solid core and forming the cover from a soft material. Neither of these proposals provide satisfactory balls because they are possible only with the sacrifice of flight performance and durability.
On the other hand, thread-wound golf balls are used by many professional golfers in a tournament because of their superior carry and controlability. However, they are poor in durability (cut resistance and fatigue resistance). Moreover, their flight performance cannot be fully exerted and they are inferior in overall distance as compared with two-piece type solid golf balls when used by amateur players. For this reason, most amateur players use two-piece type solid golf balls.
For the improvement of thread-wound golf balls in overall distance when used by amateurs, there has been proposed an idea of replacing the core with the one which is lighter and larger in diameter and replacing the cover with the one having a higher specific gravity, thereby increasing the moment of inertia (Japanese Patent Laid-open No. 129072/1984). Despite this proposal, the conventional thread-wound golf balls are not comparable to two-piece type solid golf balls in overall distance and durability.
Accordingly, there has been a demand for golf balls which have as long overall distance and durability as solid golf balls and as good controlability and shot feeling as thread-wound golf balls. Nevertheless, almost no proposals have been made for such golf balls. The present invention was completed to meet the need.